1. Field of the Invention
The present invention relates to an ink jet recording apparatus. In detail, the ink jet recording apparatus comprises a buffer tank, a mechanism for removing bubbles, and a head unit. The buffer tank contains ink to be supplied to the ink jet head. The mechanism for removing bubbles removes bubbles mixed into the ink, and is located between the buffer tank and the ink supply source.
2. Description of Related Art
Ink jet recording apparatuses that eject ink onto a recording medium based upon input signals have been known and extensively used in the art. One type is an ink jet recording apparatus in which ink from the ink source is delivered to an ink jet head through a buffer tank. The ink is directed to a plurality of ink channels in the ink jet head, and ink is ejected from nozzles in the tip of the ink channels by activation of an actuator such as a heat-generating device or a piezoelectric device. For example, as shown in Japanese Patent Application Publication NO.2001-260388, ink is supplied from the ink source to the buffer tank through a tube. Bubbles mixed in the ink are separated from the ink in the buffer tank, and ink is then supplied to the ink jet head. Furthermore, bubbles accumulated in the buffer tank are expelled to either a waste ink tank or they are returned together with ink to the ink source.
There are several methods of supplying ink to the ink jet head. One method consists of installing a cartridge containing ink on the ink jet head and supplying ink to the ink jet head from the ink cartridge. Another method involves connecting an ink tank to a buffer tank through a tube. Ink is supplied from the ink tank through the buffer tank. In this case, the tube connecting the ink tank and the buffer tank is normally a flexible resin tube. Air can permeate through the walls of this tube, and mix with the ink flowing within the tube, and form bubbles.
According to Japanese Patent Application Publication NO.2001-260388, ink is supplied from a sub-tank to the buffer tank through an ink introduction port that is formed in the top wall of the buffer tank and that projects downward into the buffer tank. Ink is introduced into the buffer tank from the lower end of the ink introduction port. The ink meanders through baffle walls so that the bubbles separate from the ink. Ink is supplied to the ink jet head through an ink outlet formed in the bottom of the buffer tank. Bubbles accumulate near the ceiling of the buffer tank, and at suitable time intervals they are removed through an outflow port by activating a pump. Also, in Japanese Patent Application Publication No. H10-315503, air buffers are provided in both the path from the sub-tank to the ink jet head and the return path from the ink jet head to the sub-tank. When following the path to the ink jet head, ink flows into the top and out through the bottom of the air buffer towards the ink jet head. Also, when following the return path, ink flows into the bottom and out through the top of the air buffer towards the sub-tank.
Also, normally ink drops are ejected from an ink jet head which has been supplied with ink from the ink cartridge installed on the head unit to which the ink jet head is fixed. However, the ink cartridge is not installed on the head unit when carrying out printing, that will consume a large quantity of ink. Rather an ink jet recording apparatus that is capable of using a large volume ink cartridge is used.
For example, U.S. Pat. No. 6,231,174 describes an ink jet recording apparatus including of a manifold that supplies and distributes ink to the ink channels on the ink jet head. Also, an ink cartridge (ink tank) is provided separated from the head unit. The manifold and the ink cartridge are connected with a flexible tube, and ink is forced to circulate between them. In this type of ink jet recording apparatus, air that permeates through the walls of the tube mixes with the ink and forms bubbles. These bubbles are introduced into the ink channels through the manifold, and cause defective ejecting. The buffer tank in the ink jet recording apparatus of Japanese Patent Application Publication NO. 2001-260388 is connected to the manifold to prevent bubbles from getting into the manifold. That is, ink is supplied from the ink tank to the ink jet head through the buffer tank and the bubbles accumulate in the buffer tank.
This type of ink jet recording apparatus is shipped from the factory with the head unit separate from the main body, or the head unit is shipped separately as a replacement item. Therefore, in order to smoothly introduce ink into the head unit the first time the head unit is installed, the head unit is filled with preservation fluid, sealed and shipped, as described in U.S. Pat. No. 6,062,390 for example.
An example of this type of ink jet recording apparatus is described in Japanese Patent Application Publication No. 2001-260388. In this ink jet recording apparatus, the ink cartridge is provided independent from the head unit. Ink is supplied from the cartridge to the buffer tank through a flexible tube, and from the buffer tank to the manifold. Ink from the manifold is supplied and distributed to all the ink channels in the ink jet head. In this type of ink jet recording apparatus, a filter is provided in order to prevent bubbles or foreign matter mixed in the ink from entering the manifold when ink is supplied from the buffer tank to the manifold.
On the other hand, Japanese Patent Application Publication No. H9-193380 describes providing an ozone treatment to the internal surface of only the manifold. The ozone treatment improves the hydrophilic nature of the internal surface so that good flow of ink to the ink jet head can be achieved.